61. 旋转链表 @Python @Go

原题

https://leetcode.cn/problems/rotate-list/description/

思路

双指针

复杂度

时间：O(n)
空间：O(n)

Python代码

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def rotateRight(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
        if not head:
            return head
        # 计算链表长度
        n = 0 
        cur = head 
        while cur:
            n += 1 
            cur = cur.next 
        # 对k取余数
        k %= n
        # 双指针
        fast, slow = head, head 
        # 移动快指针
        for i in range(k):
            fast = fast.next
        # 移动双指针
        while fast.next:
            fast = fast.next 
            slow = slow.next 
        # 旋转链表
        fast.next = head
        fast = slow.next 
        slow.next = None 
        return fast
        

Go代码

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func rotateRight(head *ListNode, k int) *ListNode {
	if head == nil {
		return head
	}
	// 计算链表长度
	n := 0
	cur := head
	for cur != nil {
		n++
		cur = cur.Next
	}
	// 对k取余数
	k %= n
	// 双指针
	fast, slow := head, head
	// 移动快指针
	for i := 0; i < k; i++ {
		fast = fast.Next
	}
	// 移动双指针
	for fast.Next != nil {
		fast = fast.Next
		slow = slow.Next
	}
	// 旋转链表
	fast.Next = head
	fast = slow.Next
	slow.Next = nil
	return fast
}